Measurement And Analysis Of Laser-induced Damage Characteristics For Ultraviolet Optics

Fused silica glass hasexcellent optical performance,its transmittance in the ultraviolet region is high,so it is widely used in light optical system,but laser-induced damageof fused silica under intense laser irradiation becomes the biggest obstacle for large-scale laser equipment to stably operate and further enhance load capacity.So achieving the accurately test and promotion of laser-induced damage threshold for UV fused silica element have important engineering significance.This paper focuses on the theory and technical issues related to the test of fused silica laser-induced damage characteristics and damage induced by sub-surface scratches,automated laser damage testing deviceis designed and built,the effect of sub-surface scratches to laser-induced damageis analyzed,the threshold enhancing duringHF acid etchingand ion beam finishing is researchedfrom a combination of theoretical and experimental point of view,the post-treatment processis explored.(1)Automated laser damage testing device according to the international standard ISO 21254 is designed and built,the damage is determined by artificial visual.The hardware includes 7 sections,for example,the laser portion,the energy attenuation system and so on,the control software isdevelopedby Labwindows to achieve control of the energy attenuation system,the shutter and the sample positioning stage.The threshold of fused silica samples is tested by 1-on-1,S-on-1,R-on-1 three ways,and the uncertainty of the threshold test is calculated.(2)The influence of scratches to laser damage of fused silicais analyzed.Nanoindentation experiments are used on fused silica to get the critical loads and critical depth of brittle–ductile transition.The light field modulation of various types of scratches is simulated by finite difference timedomain(Finite Difference Time Domain,FDTD),for typical fractures,the larger the width/depth ratiois,the weaker optical field modulation effects are,the results providean evaluation for subsequent experimental work.Typical scratches are selected to test the thresholdby R-on-1 to verify simulation conclusions.(3)The scratches morphology evolution and variation of threshold during the HF acid etching and Ion Beam Finishing are researched,the scratches are passivated during both two processes,the width/depth ratio increases,contour becomes smooth,LIDT increases,thedifference is that the IBF does not lead to the increase of scratch depth.Mathematical models of surface roughness and the threshold during the layer by layer removal process are established,too.